Air knife and vacuum doctoring apparatus



R. S. SHAFFER Aug. 25, 1970 AIR KNIFE AND VACUUM DOCTORING APPARATUSOriginal Filed Jan. 19. 196'? 2 Sheets-Sheet l INVENTOR Robe/'1 5.5/)0/20' Aug; 25, 1970 R. s. SHAFFER AIR KNIFE AND VACUUM DOCTORING APPARATU 2 Sheets-*Sheet 2 Original Filed Jan. 1.9. 1967 INVENTOR RobcrlS. Skaf/br United States Patent O 3,525,116 AIR KNIFE AND VACUUMDOCTORING APPARATUS Robert S. Shaffer, Glen Burnie, Md., assignor toBethlehem Steel Corporation, a corporation of Delaware Originalapplication Jan. 19, 1967, Ser. No. 610,400. Divided and thisapplication Mar. 12, 1969, Ser. No. 841,164

Int. Cl. A471 /38 US. Cl. 15-306 6 Claims ABSTRACT OF THE DISCLOSUREAspirating devices are positioned adjacent the edges of sheet or strippassing from a molten coating bath between gas wiping dies to draw gasaway from the edge of the sheet and thereby prevent edge buildup.

BACKGROUND OF THE INVENTION This is a division of application Ser. No.610,400, filed Ian. 19, 1967.

This invention is directed to the treatment of moving sheet having amolten coating thereon to provide a uniform coating across the width ofthe strip.

Gas wiping arrangements for smoothing the molten coating on sheetleaving molten metal coating baths have been used to replace the moreconventional exit roll arrangements in such baths. These so-called jetwiping arrangements provide a more even coating on the sheet and willoperate efficiently on very fast moving sheet. As with the older exitrolls, however, difficulty has been experienced with so-called edgebuildup, a tendency to form heavier coatings near the edges of the sheetthan are formed on the central portions of the sheet. The sameexpedients have been tried to eliminate this edge buildup with jetwiping devices as have been used to alleviate edge buildup with exitrolls, but without notable success.

SUMMARY OF THE INVENTION I have discovered that edge buildup on sheetbeing coated in a molten metal bath and smoothed by means of a gaswiping arrangement can be reduced or eliminated by means of aspiratorspositioned adjacent the edges of the sheet which draw gases away fromthe edge of the strip. I hypothesize that such aspiration acts byreducing gas turbulence in the vicinity of the sheet edges.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a molten metalcoating bath apparatus incorporating the present invention.

FIG. 2 is a sectional side view portion of the apparatus taken alongline 2-2 of FIG. 1.

FIG. 3 is an enlargement of a portion of the apparatus shown in FIG. 1including a sectional view of the aspirating device of the presentinvention.

FIG. 4 is a top view of the apparatus of FIG. 3 viewed along line 4-4.

FIG. 5 is a top view of a potrion of the mounting arrangement of theapparatus viewed along line 55 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings amolten metal bath 11 is held in a conventional pot 13. A sinker roll 15is submerged in the molten bath 11 journaled in some suitable supportingmeans not shown. A metallic sheet or strip 17 to be coated with themetal of the bath is passed into the bath 11 around sinker roll 15 andout of the bath between gas wiping dies 19 and 21 mounted on supportingmeans 23 attached to I-beam supports 25 and 26 mounted above bath 11upon side supporting structure 27 attached to side columns 29. Astructural channel 31 is mounted upon I-beam support 25.

Gas wiping dies 19 and 21 are hollow and have narrow slots 33 alongtheir forward edges through which any suitable gas such as hot air,steam, or the like is forcibly expelled in a thin sheet extending acrossthe width of the strip to wipe excess molten metal from the strip andsmooth the molten coating remaining thereon. The gas is admitted to thedies 19 and 21 through three inlet pipes 35 connected to each wipingdie. The slots 33 are aligned with each other on opposite sides of thestrip 17 in order to prevent the strip from being forced to either sideby the force of the gas blast.

Dies 19 and 21 normally extend a little beyond the edge of the strip 17on each side in order to thoroughly wipe the strip across its entireface and also to allow for minor variations in the tracking of thestrip.

Aspirating devices 37 and 39 are monuted adjacent each strip edgecoplanar with wiping dies 19 and 21. Each aspirating device is supportedon the lower end of a pipe 41 through which compressed air or othersuitable gas or even liquid is fed from any suitable source, not shown,through flexible hose 43. Pipe 41 passes through a fulcrum member 45 inwhich it is secured at an appropriate level by a set screw 47. Fulcrummember 45 is mounted in a fulcrum assembly 49 comprising an angle 51having a side 53 and a bottom 55 to which are secured two L- shapedfulcrum supports 57 and 59. Pipe 41 passes through an opening 54 inbottom '55 of angle 51 with sufficient clearance to allow transversemovement of the pipe. Fulcrum 45 rests on the bottom legs 57A and 59A ofboth fulcrum supports 57 and 59 and is urged into a partial circularcut-out section in the side legs 57b and 59b of the L-shaped fulcrumsupports by a movable keeper bar 61 pivoted on a bolt 63 secured throughside 53 of angle 51. The contacting surfaces between fulcrum 45, fulcrumsupports 57 and 59, and keeper bar 61 may all be greased so that fulcrum45 is free to pivot with the application of only a small force. Angle 51of fulcrum assembly 49 is clamped in position transversely of channel 31as shown in FIGS. 2, 3, and 5 by means of clamping plates 65 and 66,which fit over one flange of channel 31, and set screw 67 threadedthrough clamping plate 65 and biased against the flange.

Attached to the bottom of aspirators 37 and 39 is a tracking bar 69 tothe end of which is attached a guide shoe 71 having a fiat bottomedV-groove 73 in one end which fits over the edge of the sheet 17. A wearbar 75 of satellite or other wear resistant material is secured to thebottom of guide shoe 71 at the bottom of V-groove 73 so that the sheetedge bears against the wear bar 75 as the strip passes upward throughthe V-groove 73 of the guide shoe 71.

Aspirator device 37 comprises two parts, an upper chamber 77 and a lowerchamber 79. Pipe 41 opens into upper chamber 77 and compressed airpassing down pipe 41 passes into chamber 77 which acts as a small plenumchamber to equalize small line surges and then passes uniformly throughslot 81 into lower chamber 79 being directed forcibly toward the rear ofchamber 79 and exiting through orifice 83 into the atmosphere. Chamber79 is also open at the front and gas and air are drawn into this orifice85 to replace the partial vacuum created by the aspirator action of thecompressed air directed rearwardly by slot 81. Gas emerging from the gaswipers 19 and 21 adjacent the edge of the sheet together with more orless entrained air is consequently drawn into orifice 85 away from thevicinity of the sheet 3 edge and expelled into the atmosphere to theside of the sheet. The continuous removal of such gas and air enablesthe wiping dies 19 and 21 to efiiciently wipe the sheet all the way tothe edge and thus effectively decreases or eliminates edge buildup.

The gas and air which is expelled from orifice 83 thrusts aspiratordevices 37 and 39 by reaction towards the sheet edge so that wear bar 75is continuously held against the sheet edge and the entire aspiratordevice pivoting on fulcrum 45 follows or maintains the same correctdistance from the sheet edge at all times regardless of tracking of thesheet or other variations.

While other designs of aspirator may also be successfully used,considerable experimentation has shown that it is very desirable to usean aspirator such as that shown, which has a relatively straight throatfrom orifice 85 to orifice 83, as the aspirator tends desirably to draw01f protruding particles and beads of metal formed along the edge of thestrip so as to form a very desirable rounded coating along the edge.These surplus molten metal particles are drawn through the aspirator andexpelled with the gas and air and, if the throat of the aspirator is notrelatively straight, will tend to form deposits on any sharp bends orcorners in the device I to such an extent as to eventually completelyclog and block the aspirator.

My explanation for the results obtained by this invention is as follows:The collision of the gas streams from the two opposing dies 19 and 21 aswell as the flow of the wiping gas around the edge of the strip createsturbulence at the edge of the strip which interferes with the wipingaction of the gas jets near the edge of the strip. This interference isat a maximum near the edge of the strip and diminishes as the distancefrom the edge increases. In addition, there is a strong air currentmoving in toward the edge of the strip as a result of the partial vacuumcreated by the Bernoulli effect of the dies. This current of airproduces additional interference with the wiping action of the gas dies.This turbulence and interference is a prime cause of edge buildup orheavy edge coatings on the strip. This turbulence and interference aregreatly decreased if not completely eliminated by drawing the turbulentair and gas away from the edge of the strip by means of theaspiratorsabove described.

The aspirators of the invention may also be used where the gas wipingdies are not coplanar with each other, or where a gas wiping die is usedto wipe only one side of a flat product. In this case, even though thereis no interference between the gas jets from opposed coplanar gas wipingdies, the edge of the product and the air stream moving in from the sidedue to the Bernoulli effect of the gas jets on one side may still causeexcessive turbulence adjacent the edge. If so, the aspirators of thepresent invention may be used to alleviate this condition. It isessential only that the aspirators be located adjacent both the edge ofthe sheet and the impingement point of the gas jets on the edge of thesheet.

By the term aspirator as used herein I mean any apparatus, as a suctionpump, exhaust fan, etc., for producing a movement of gases by suction.

I claim:

1. Apparatus for providing an even coating substantially without edgebuildup on moving sheet coated with an unsolidified coating materialcomprising:

(a) gas wiping means transverse of the movement of said sheet to wipe atleast one side of the sheet as it passes said wiping means, and

(b) aspirator means mounted adjacent at least one edge of said sheetsubstantially in the plane of the sheet and spaced transverselytherefrom and adjacent said gas wiping means to draw gas away from theedge of said sheet.

2. Apparatus according to claim 1 in which there are opposed gas wipingmeans on opposite sides of said product.

3. Apparatus according to claim 1 in which said aspirator has entranceand exit orifices and a substantially straight passage between theentrance and exit orifices.

4. Apparatus according to claim 1 in which said aspirator is movablymounted and discharges gaseous materials away from the strip so as tocontinuously bias the said device by reaction toward the strip edge.

5. Apparatus according to claim 4 wherein the aspirator has entrance andexit orifices and a substantially straight passage between said entranceand exit orifices.

6. Apparatus according to claim 5 wherein there are opposed coplanar gaswiping means spaced on opposite sides of said product.

References Cited UNITED STATES PATENTS 1,385,042 7/1921 Decker et al.118-63 X 2,894,856 7/1959 Schwendemann et al. 1l8-63 X 2,899,339 8/1959Rakus 11863 X 3,045,273 7/ 1962 Bruno 15-306 3,239,863 3/1966 Gardner15-345 X 3,370,982 2/1968 Hayunga 15306 X 3,374,118 3/1968 Seress et al.15-345 X MORRIS KAPLAN, Primary Examiner US. Cl. X.R.

